1. Field of the Disclosure
The technology of the disclosure relates to optical fibers, and in particular, angle-cleaved optical fibers for use in monitoring of optical light sources.
2. Technical Background
Optical fibers can be used to transmit or process light in a variety of applications. Examples include delivering light to or receiving light from integrated optical components or devices formed on substrates, transmitting information channels in wavelength-division multiplexed optical communication devices and systems, forming fiber optic switch matrix devices or fiber array to array connectors, and producing optical gain for optical amplification or laser oscillation. Optical fibers essentially operate as “light pipes” to confine light within the fiber boundary and transfer light from one point to another.
A typical optical fiber may be simplified as having an optical fiber core and a cladding layer surrounding the optical fiber core. The refractive index of the optical fiber core is higher than that of the cladding to confine the light. Light rays coupled into the optical fiber core within a maximum angle with respect to the longitudinal axis of the optical fiber core are totally internally reflected at the interface of the optical fiber core and the cladding. Total internal reflection (TIR) is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index of the material on the other side of the boundary is lower, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs. This TIR spatially confines the optical energy of the light rays in one or more selected optical fiber modes to guide the optical energy along the optical fiber core.
Optical links for short distance applications (e.g., <1 km) may employ multimode optical fibers for relaxed alignment tolerances to sources and detectors. The large size of the multimode optical fiber core makes the optical interconnections highly tolerant of lateral, angular and axial misalignments with respect to Fabry-Perot or Vertical Cavity Surface Emitting Laser (VCSEL) laser sources. For this and other reasons, it is sometimes desired to monitor the amount of light propagating in an optical fiber. For example, eye safety requirements for a given optical link may dictate that optical fiber power levels not exceed a predefined maximum level. At the same time, the optical power received at the detector should be greater than a desired minimum level to avoid or minimize bit errors due to detector noise. Optical sources launch an optical signal into the optical fiber at power levels to keep the link optical power at a power level between desired maximum and minimum levels. Moreover, as lasers age, the amount of light they produce may slowly change under constant laser drive conditions. A solution in source-to-fiber coupling applications involves positioning a detector near the laser source to monitor the light coming from the laser source. A fraction of the optical power is directed to the detector to monitor output power levels over the life of the laser.
It is desired to have a scheme for monitoring the amount of light propagating in an optical fiber that may be employed at an arbitrary location along an optical fiber and that may be implemented in a compact form.